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Organometallics 1990, 9, 534-536
bonded.26 'H NMR and 13C NMR resonances for the methylene group of 7 are located a t 1.98 and -2.3 ppm, respectively. These values compare favorably with those for the (benzofu1vene)-and (fu1vene)diiron hexacarbonyl c~mplexes.~~~~' Our current work includes efforts to improve the yields of 6, a crystal structure, and chemical studies. We will report on these in due course.
061
Acknowledgment. We acknowledge the donors of the Petroleum Research Fund, administered by the American Chemical Society, for financial support. We thank Dr. George Crull for helpful NMR consultations. We also thank Christopher Pisani for help in the large-scale synthesis of 2-methylindene. Registry No. 6, 124511-84-8; 7,49596-01-2; 2,3-dihydro-lHinden-2-one, 49596-01-2; 2-methyl-2,3-dihydro-lH-inden22-ol, 33223-84-6; 2-methyl-lH-indene, 2177-47-1; 3-bromo-2-bromomethyl-1H-indene,60858-22-2;[~4-5,6-bis(methylene)-l,3-cyclohexadiene]tricarbonyliron, 12181-95-2. (26) Victor, R.; Ben-Shoshan, R. J. Organomet. Chem. 1974,80, C1-4. (27) Koch, 0. Dissertation; Hamburg, FRG, 1980. Cf.: Gmelin 1 Handbuch der Anorganischen Chemie; Springer-Verlag: New York, 1981; Organo Iron Compounds, Vol. C5, p 9. Data for (fu1vene)diiron hexacarbonyl:
U 4
3
lH NMR (CgDg,6): 1.85 ( 8 , CH,); 4.01 (t, H1,3); 4.93 (t, H5,4). ' 9NMR (6): 212.8 (CO); 94.5 (C2); 84.2 (C4,5);75.6 (C1,3); -3.1 (C6). IR (Cyclohexane): v(C0) = 2077, 2014, 2004, 2000, 1981, 1950 em-'. (28) Cooper, M. A.; Elleman, D. D.: Pearce, C. D.; Manatt. S. L. J. Chem. Phvs. 1970.53.2343-52. (29) Biilig, W.; Wendt, J.; Patt, D.; Gresch, E.; Singer, H. J. Organomet. Chem. 1988,338, 227-35. (30) Roth, W. R.; Meier, J. D. Tetrahedron Lett. 1967, 22, 2053-8. (31) Bovey, F. A. Nuclear Magnetic Resonance Spectroscopy; Academic Press: New York, 1969.
Synthesis and Characterization of the Chiral Cluster Fe3(CO),[q3-B( H)C( H)C( Me)]. An Unamblguous Example of a Transitlon-Metai-Maln-Group Six-Atom Cluster Xlangsheng Meng and Thomas P. Fehlner' Department of Chemistty, University of Notre Dame Notre Dame, Indiana 46556
Arnold L. Rhelngold" Department of Chemistry, University of Delaware Newark, Delaware 19716 Received October 6, 1989
Summary: The synthesis and structural characterization of the first example of a boracyclopropene ring coordinated to a trimetal fragment, Fe3(CO),[C3-B(H)C(H)C(Me)], I, are described. The compound constitutes an example of a cluster containing three transition metals that can only be reasonably considered as a six-atom cluster containing three iron, two carbon, and one boron atoms. This particular derivative of the cluster core also constitutes an example of a chiral cluster.
Figure 1. Structure and labeling scheme of Fe3(CO)9[s3-B(H)C(H)C(Me)],I. Atoms are shown as 30% thermal elhpsoids except hydrogen atoms, which are drawn at a fixed radius. One of two crystallographicallyindependent but chemically similar molecules is shown.
The relationship between main-group and transitionmetal clusters is expressed in the electron-counting formalism that has been developed over the past 10 or 15 years.l Although the reality of these rules lies in their usefulness, the study of compounds containing both transition-metal and main-group atoms in a contiguous network serves to emphasize similarities and differences in bonding of homonuclear clusters of atoms with and without d valence orbitals. However, in these mixed main group-metal systems an ambiguity often arises in the sense that a molecule containing n metal atoms and m maingroup atoms can be equally well considered as an n + m atom cluster or an n atom cluster with a qm ligand. Herein we report the characterization of a molecule that can only be reasonably considered a six-atom cluster containing equal numbers of main-group and transition-metal atoms. The new compound was prepared via a developing method2 for the synthesis of metallaboranes and metallacarboranes via the reaction of organometallic compounds, particularly those containing negatively charged ligands, with boranes. Specifically, the new cluster was synthesized from the reaction of [Fe(Py),] [Fe4(C0)13]3with BH2Br. SMe2in toluene at 75 OC for 2 h. After removal of toluene under reduced pressure, protonation of the residues with CF3COOH and hexane was followed by low-temperature chromatography. Fractional crystalization of the second band (brown) containing mainly [HFe4(CO)12C]BH24 gave bright red crystals of a new compound in about 5% yield. The spectroscopic data5 indicate that the compound can be formulated as Fe3(C0),[q3-B(H)C(H)C(Me)],I. Our approach usually produces compounds with either reduced (1)Wade, K. Inorg. Nucl. Chem. Lett. 1972,8, 559. Wade, K. Adv. Inorg. Chem. Radiochem. 1976,18,1. Mingos, D. M. P. Nature, Phys. Sci. 1972, 236, 99. Mingos, D. M. P. Acc. Chem. Res. 1984, 17, 311. (2) Fehlner, T. P. New J. Chem. 1988, 12, 307. Meng, Xiangsheng. Ph.D. Thesis, University of Notre Dame, 1990. (3) Whitmire, K.; Ross, J.; Cooper, C. B.; Shriver, D. F.; Inorg. Synth. 1982, 21, 66. (4) Meng, X.; Rath, N. P.; Fehlner, T. P. J.Am. Chem. SOC. 1989,111, 3422. Meng, X.; Rath, N. P.; Fehlner, T. P.; Rheingold, A. L. Abstr. X X V I I Int. Conf. on Coord. Chem. Gold Coast, Australia, July 2-7,1989. (5) IR (hexane, cm-') 2560 w (BH), 2090 m, 2040 vs, 2035 vs, 2020 8 , 2005 m, 1985 w (sh) (CO); 'lB NMR (hexane, 20 "C) 6,58.2 (d, J ~ =H 177 Hz); 'H NMR (CDZCl,, 20 "C) 6 7.82 (8, CH, 1H), 6.02 (q, Jg" e 190 Hz,1 H), 2.53 (8, CH3, 3 H); 13CN M R (CDZC12, 20 OC, ('HI) 8 210.4,209.5, 209.3 (s, 9 CO), 187.5 ( 8 , CMe),164.4 (8, CH),40.8 ( 8 , CMe); MS (EI)Pc = 472 (-9CO); 56Fe312C12'60911Bl'H~', 471.8087 obsd, 471.8078 calcd.
0276-7333/90/2309-0534$02.50/00 1990 American Chemical Society
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Organometallics, Vol. 9, No. 2, 1990 535
Table I. Selected Bond Distances a n d Angles for I (a) Bond Distances, A Fe( 1)-Fe(2) 2.605 (2) Fe(1)-B 2.010 (11) 2.552 (2) Fe(2)-B Fe(2)-Fe(3) 2.046 (11) 2.586 (2) Fe(l)-C(IO) 1.995 (11) Fe(l)-Fe(3) 2.008 (8) Fe(2)-C(11) 2.003 (9) Fe(3)-C(10) 1.502 (14) 2.020 (7) C(ll)-C(lO) Fe(3)-C(11) 1.597 (15) C(IO)-B 1.596 (15) C(II)-B Fe(P)-Fe(l)-Fe(3) Fe(3)-Fe( 1)-B Fe(2)-Fe( 1)-B Fe(I)-Fe(S)-Fe(S) Fe(3)-Fe(2)-C(ll) Fe( 1)-Fe(2)-B Fe(3)-Fe(2)-B Fe(l)-Fe(3)-C(10) Fe(2)-Fe(3)-C(ll) Fe(l)-C(lO)-C(ll) Fe(l)-C(IO)-B C(Il)-C(IO)-B Fe(2)-C(Il)-C(IO) Fe(2)-C( 11)-B Fe(1)-B-Fe(2) Fe(2)-B-C(10) Fe(2)-B-C(11) c(10)-C(11)-C(12) Fe(3)-C(Il)-C(12) C(IO)-C(II)-B
(b) Bond Angles, deg 58.9 (1) Fe(S)-Fe(l)-C(lO) 77.4 (3) Fe(l)-Fe(l)-C(IO) 50.6 (3) C(IO)-Fe(l)-B 60.2 i i j 50.9 (2) 49.4 (3) Fe( I)-Fe(3)-Fe(2) Fe (2)-Fe(3)-C (IO) 77.6 (3) 49.5 (3) Fe(l)-Fe(B)-C(Il) 50.3 (3) C(lO)-Fe(3)-C(11) 106.3 (7) Fe(3)-C( 1O)-C(11) 67.0 (6) Fe(3)-C(IO)-B 62.0 (7) Fe(2)-C(ll)-Fe(3) 105.7 (6) Fe(3)-C(ll)-C(lO) 68.2 (5) Fe(3)-C(Il)-B 79.9 (3) 100.3 (6) 65.4 (5) 124.6 (9) 127.9 (6) 61.9 (7)
74.0 (3) 50.0 (3) 47.0 (4) 74.0 (3) 46.4 (4) 60.9 (1) 75.0 (3) 74.2 (3) 43.8 (4) 68.5 (4) 107.0 (6) 78.7 (3) 67.7 (4) 106.4 (6) 66.0 (5) 101.9 (5) 56.1 (6) 128.4 (7) 124.2 (6)
carbone or inserted boron.7 Occasionally it has yielded compounds containing both boron and reduced carbon, e.g., [HFe4(C0)12C]BH24 and HFe3(C0)9(H3BCH3),7but in these cases either the boron or the carbon atom are found in a cage substituent. The result of X-ray crystallographic analysis has shown that the new compound contains a typical triangular Fe3(CO)gfragment apparently v3-coordinated to a threemembered heterocyclic ligand containing one boron atom such that the borirene ring is almost (1.2' deviation) coplanar with the triiron plane, thereby forming a "Star of David" as shown in Figure 1.8 Selected bond distances and angles for I are given in Table I. As free trimesitylborirene has been fully characterized? the obvious initial way of viewing I is as a borirene ligand bound v3 to a Fe3(CO)gfragment. In this regard the metal fragment in I is not unlike that in Os3(C0)9(v3-CeHe).'o The ring of free trimesitylborirene is an equilateral triangle with an edge length of 1.42 A. In I the boron-carbon (1.596 (15) and 1.597 (15) A) and carbon-carbon (1.502 (14) A) bond distances are unequal but normal for single B-C and C-C bonds." Coordination of r ligands usually results (6) Wong, K. S.; Haller, K. J.; Dutta, T. K.; Chipman, D.; Fehlner, T. P. Inorg. Chem. 1982,21, 3197. (7) Vites, J.; Housecroft, C. E.; Eigenbrot, C.; Buhl, M. L.; Long, G.
J.; Fehlner, T. P. J. Am. Chem. Soc. 1986,108, 3304. (8) Crystal data: C12H6B,0gFeS;triclinic, Pi, a = 8.120 (1) A, b = 13.717 (3) A, c = 15.620 (2) A, a 104.45 (I)', f l = 101.61 (I)', y = 96.63 (1)O, V = 1624.9 (5)A3,2 = 4; D(calcd) = 1.927 g cm"; ~ ( M Ka) o = 26.86 cm-l; T(max)/T(min) = 1.60; temp = 23 "C; Nicolet R3m/p, Mo Ka. Of 5955 empirically absorption-corrected data (4' 5 28 5 50') (Lamina corrections, 3O glancing angle, face index = 010) 5326 were independent (R, = 3.23%) and 3344 were observed (5u(FJ). The structure was solved by direct methods which located the iron atoms. Subsequent leastsquares refinement located the remaining atoms. The asymmetric unit consists of two independent molecules, one fully ordered, the other showing possible disorder in the B' and C(l0') sites; the thermal parameters and bond metrics for these atoms do not show the distinct differences seen in the molecule with unprimed atoms. All non-hydrogen atoms were refined anisotropically, all hydrogens idealiied (d(CH) = 0.96 A; U, = 1.2Uc). R(F) 5.2%, R(wF) 5.45%, GOF 1.282, /.L~//I,, 7.23, A/u(final) = 0.168, A(p) = 1.271 e A-s. SHELXTL, software used for all computation (Nicolet XRD, Madison, WI). 1987, (9) Eisch, J. J.; Shafii, B.; Rheingold, A. L. J. Am Chem. SOC. 109, 2536. (IO) Gomez-Sal, M. P.; Johnson, B. F. G.; Lewis, J.; Raithby, P. R.; Wright, A. H. J. Chem. Soc., Chem. Commun. 1985, 1682.
in an increase in bond distances, thus, in terms of geometric changes, consideration of I as a polyhapto ligand bound to a trimetal fragment is acceptable. However, this view of I creates a problem in counting electrons. The Fe3(CO)gfragment requires six electrons to become saturated, while the borirene ligand has only two electrons to donate. Hence, I would constitute a presently unknown example of a 44-electron trimetal cluster. While not impossible, one would expect to observe short Fe-Fe distances reflecting an unsaturated metal framework. On the contrary, the observed Fe-Fe distances [2.605 (2), 2.586 (2), and 2.552 (2) A] must be considered long, if anything. Alternatively, one notes that the core of I forms a severely distorted octahedron. As the Fe(C0)3fragment is isolobal with the BH fragment, I is electronically analogous to 1,2-C2B4H6.11Further I is analogous to (C5H5)3C03B3Hence, I can be easily H,12 as well as recognized as a closo cluster containing seven skeletal electron pairs.' For this reason, it should be considered unsaturated or "electron deficient" in the same sense that [B6H6I2-or [Ru&C0),,l2- is unsaturated. Consistent with this view is the fact that the B-C and C-C distances are very similar to those reported for 1,2-CzB4He11and the Fe-Fe distances are similar to those for [Fee(C0)16C]2-.14 In fact, consideration of I as a three-member ring bound q3 to a trimetal fragment makes as much or little sense as considering [B6H6I2-(or [Ry(C0)18]2-)as two [B3HB]-(or [Ru~(CO)~]-) rings bound fa~e-to-face.'~Clearly, in the homonuclear clusters the irreducible element of bonding is the six-member octahedral framework. Although it is hidden by the distorted nature of the octahedral core, the minimal bonding element of I, too, is a six-member closed cage. Further, compound I constitutes an example of a chiral metallacarborane cluster. The first chiral clusters containing a triangular array of three different metal atoms with a capping main-group element were reported in 1980l6 and have considerable potential significance as mechanistic probes and ~at1aysts.l~The use of chiral organometallic complexes as enantioselective or optical induction catalysts for asymmetric synthetic reactions has been developed in the past two decades.18 Although the formation of the chiral compound I was serendipitous rather than planned, the compound now provides an example of chirality supplied by the main-group portion of the cluster rather than by ligands on the metallg or by different metals.16 Since each of the six vertices of I can be considered as a chiral atom, such a cluster may be even more effective than the monocapped trimetal cluster.16 However, before any applications of asymmetric reactivity can be envisioned, the (11)Onak, T. In Boron Hydride Chemistry; Muetterties, E. L., Ed.; Academic: New York, 1975; p 349. (12) Pipal, J. R.; Grimes, R. N. Znorg. Chem. 1977, 16, 3255. Miller, 1976,98, 1600. V. R.; Grimes, R. N. J. Am. Chem. SOC. (13) Johnson, B. F. G.; Lewis, J.; Reichert, B. E.; Schorpp, K. T.; Sheldrick, G. M. J. Chem. Soc., Dalton Trans. 1977, 1417. (14) Churchill, M. R.; Wormald, J. J. Chem. Soc., Dalton Trans. 1974, 2410. (15) We have previously commented upon the usefulness of considering main-group and transition-metal atoms as constituting the cluster cage. Fehlner, T. P.; Housecroft, C. E.; Wade, K. Organometallics 1983, 2, 1426. (16) Richter, F.; Vahrenkamp, H. Angew. Chem., Znt. Ed. Engl. 1980,
19'165.
17) Vahrenkamp, H. J. Organomet. Chem. 1989,370,65. 18) Knowles, W. S.; Sabacky, M. J. Chem. Commun. 1968, 1445. Special Volume on Organometallic Compounds and Optical Activity: J. Organomet. Chem. 1989, 370. Bosnich, B. Chem. Br. 1984, 20, 808. Aratani, T.; Yonuyoshi, Y.; Nagase, T. Tetrahedron Lett. 1977, 2599. Otsuka, S.; Noyori, R.; et al. In Asymmetric Reactions and Processes in Chemistry; Eliel, E. L., Otsuka, S., Eds.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985; No. 185, p 186. (19) McGlinchey, M. J. Organometallics 1987, 6, 439.
Organometallics 1990, 9, 536-537
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optical resolution of the enatiomers of I must be achieved.
Acknowledgment. The support of the National Science Foundation under Grant CHE87-01413 and The Army Research Office under Contract DAAL03-86-K-0136 are gratefully acknowledged. Supplementary Material Available: Tables of crystal data, atom coordinates,bond distances and angles, anisotropic thermal parameters, and H atom coordinates (7 pages);tablea of observed and calculated structure factors (20 pages). Ordering information is given on any current masthead page.
. .
Core Conformational Rearrangement Accompanying Two-Center, Blmetalllc Redox Reactlons. Chemlcal and Structural Properties of the Pyrazolyl-Bridged Rhodlum Dlmers [Rh( $-C,Me,)CI(p-pz)], and [Rh(sS-CSH$)(P-Pz)12 James A. Bailey, Stephen L. Grundy, and Stephen R. Stobart’
c19
CIS
Department of Chemistw, University of Victoria Victoria, British Columbia, Canada V8 W 2Y2 Received September 22, 1989
,
Summaty: Reaction between [Rh($-C,Me,)CI(p-pz)] (9, which exhibits a “chair” conformation for the core pyrazolyl-bridged bimetallic unit in the crystal with Rh, separation 4.059 (2) A, and AgBF, affords [Rh,($-C,Me,),(ppz),(p-CI)]BF, (6), in which the cation core exists in a “boat” conformation with Rh centers 3.588 (2) A apart: reduction (Zn/Cu) of 5 yields a purple product (7) tentatively identifM as [Rh($C,Me,)@-pz)],, the bright purpie, reactive v5-C,H5 analogue 9 of which has been synthesized from [Rh(l15-C5H5)CI(p-pz)],(8) and shown by using single-crystal X-ray diffraction to possess a deeply foMed (“boat”) geometry in which Rh-Rh = 2.657 (3) A. ORTEP drawings of (top) [Rh(v6-C5Me5)C1(p-pz)1, (5) showing the “chair”conformation about the six-memberedmetallacycle, (middle)the cation in ([Rh(v5-C,Me5)(r-pz)]2GL-Cl)1BF, (6) showing the “boat” conformation, and (bottom) [Rh($(9). Selected bond distances (A) and angles (deg; C~H&LL-PZ)]~ 4 is cp ring centroid): compound 5, Rh-Rh’ 4.059 (2); Cl(l)-Rh 2.399 (2);N(l)-Rh 2.105 (7);N(2)”Rh 2.110 (7);$-Rh 1.782 (10); N(l)-Rh-Cl(l) 89.6 (2); NQ)’-Rh-N(l) 90.8(2);N(2)’-Rh-C188.5 (2); 4-Rh-Rh’ 131.6 (3);compound 6, Rh-Rh’ 3.588 (2); C1-Rh 2.378 (2); N(l)-Rh 2.081 (7); N(2)’-Rh 2.101 (9);4-Rh 1.777 (2); N(l)-Rh-C188.3 (2); Rh-Cl-Rh’ 97.9 (1);N(P)’-Rh-N(l) 79.9 (2); N(Z)’-Rh-Cl 88.0(2); 4-Rh-Rh’ 163.8 (2); compound 9, Rh(2)Rh(1) 2.657 (3); N(l)-Rh(l) 2.04 (3); N(3)-Rh(l) 2.06 (2); N(2)-Rh(2) 2.00 (2); N(4)-Rh(2) 2.02 (2); d(l)-Rh(l) 1.84 (3); 6 (2)-Rh(2)1.83 (3);N(l)-Rh(l)-Rh(2) 70.7 (7); N(3)-Rh(l)-Rh(2) 70.7 (7); N(3)-Rh(l)-N(l) 83.4 (9); N(2)-Rh(2)-Rh(l) 72.4 (7); N(4)-Rh(2)-Rh(l) 69.3 (6); N(4)-Rh(2)-N(2) 86.1 (10); 4(1)Rh(l)-Rh(2) 131.7 (9); @(2)-Rh(2)-Rh(l)135.2 (9). Estimated standard deviations are given in parentheses.
Figure 1.
Concurrent activation of linked coordinatively unsaturated transition-metal centers, which may mediate critical steps in a range of natural and artificial catalytic cycles, is an emergent area of bimetallic chemistry for which so far only very sketchy mechanistic definition exists. We have found that in the family of diiridium(1) complexes [IrL’L2(p-pz)]2(1, L’L2 = COD, cycloocta-l,Bdiene, pzH = pyrazole; 2, L’ = L2 = CO; 3, L’ = CO, L2 = PPhJ the pyrazolyl ligands are unusually flexible in bridging, accommodating major alterations in intermetallic separation along the Ir, axis.’ Thus multisite redox reactions that are accompanied by metal-metal bond formation or fracture can proceed without disruption of the integrity of the cyclic bimetallic core.2 Weak metal-metal interactions characteristic3 of binuclear structures like those of 1-3 may act to constrain the geometry of the bridged framework (accounting, e.g., for the conformational rigidity of dimer 1, where COD CH2 resonances remain distinguishable in ‘H or 13C NMR spectra even at elevated temperature); but whether ring inversion facilitates formation of axially substituted diiridium(I1) products is not known, although it is a logical mechanistic idea. In fact to date the extensive redox associated with (1) Coleman, A. W.; Eadie, D. T.; Stobart, S. R.; Zaworotko, M. J.; Atwood, J. L. J. Am. Chem. SOC.1982, 104, 922. (2) Atwood, J. L.; Beveridge, K. A.; Bushnell, G. W.; Dixon, K. R.; Eadie, D. T.; Stobart, S. R.; Zaworotko, M. J. Inorg. Chem. 1984,23,4050.
compounds 1-3 has connected exclusively geometries that exist in ”boat” conformations (including t h 0 d 5 that afford d62products as cofacial bioctahedra). In examining further the d72:ds2 redox manifold (i.e., that connecting the met(3) Brost, R. D.; Fjeldsted, D. 0. K.; Stobart, S. R. J. Chem. SOC., Chem. Commun. 1989, 488. (4) (a) Harrison, D. G.; Stobart, S. R. J. Chem. SOC.,Chem. Commun. 1986,285. (b) Brost, R. D.; Stobart, S. R. J. Chem. SOC.,Chem. Commun. 1989,498. (5) Fjeldsted, D. 0. K.; Stobart,S. R.; Zaworotko, M. J. J. Am. Chem. SOC.1985, 105,8258.
0276-7333f 90f 2309-0536$02.50 f 0 0 1990 American Chemical Society
